Cove cutting with TS

[D L Ames]

Does anyone have any advise or wisdom to share on cutting coves with the tablesaw. I have used this technique before on a very limited basis but would like to expand my knowledge on this technique.

Here is a set up I have used before to cut some coves on the top and bottom of some boxes I built.



In this case I clamped the fence up 45 degrees to the blade and ran my material through multiple passes raising the blade 1/16" for each pass.

This set up worked great for what I needed at the time but I understand you can use a similar set up to cut a full cove down the center of a board. I am just not sure how to set up the fence to make a full cove cut. A while back I read an article that mentioned you can change the shape (depth, width) of the cove by changing the angle of the fence to the blade.

Also, this technique requires a lot of sanding afterwards to remove the machine marks. Has anyone ever tried this technique using a molding head with a radius type cutter? If so, where the result any smoother?

I look forward to any advice that can be offered or discussion generated.

D L

[chris99z71]

Now don't take this as gospel because I've never tried it, but it seems that in order to get it down the middle of the board, you'd have to have your fence farther back from the blade (away from the user). Far enough that the blade doesn't contact the fence. Does this make any sense?

[Monty]

I would think you need two fences - front and back, to hold the workpiece securely. Or a fence and featherboards. You can change the profile of the cove by altering not only the angle of the fence, but also the tilt of the blade. Get down on the level of the table saw surface and sight down the blade parallel to the fence to get an idea what the profile will look like with various changes in blade tilt/fence angle. Basically, tilting the blade will just move the apex of the cove over, creating a larger radius on one side and a tighter radius on the other side. There is also a parallelogram jig that can help with setting the fence angle.

There is an excellent web site on this subject here.

[chris99z71]

Good link Insomniac! Now I can start thinking about a molding head cutter...must...resist...urge...AHHHHH!!!!
I believe I'm entering the advanced stages of woodguy disease, no...molding head cutters are under 1000lbs...

[Big Mike]

I agree with Insomniac, use the double guide board method and whatever you do use push sticks and pads. One of my closest woodworking friends just ran fingers though a window molding bit on the router table over the weekend. To me the coving operation is a dangerous operation under any circumstances and I always recommend using push pads to control the stock, no hands!

I also recommend using a nice sharp 50 tooth combination blade. Let's be careful out there

[Joe Scharle]

As you've already discovered it's a long, slooooow process. When I've had to do it (not often, because if I can buy a pre milled molding, I will) I'll hog out as much of the waste as I can with a dado blade or molding set fed straight on using the saw fence. Then my finish pass will be between 2 board fences set at whatever angle that allows the front and rear of the piece to pass the same tooth of my regular sawblade. Leave yourself plenty of wood between the top of the cove and the flat part you're pushing down on. It's scary when the board snaps halfway through the blade. The millmarks are a pain. I used 2-3 flutter sets on my drill before I got it to the point I could hand sand with paper wrapped around a big round turning. Good luck

Joe

[Big Mike]

DL, I failed to answer part of your question. No, I have never used a molding head cutter but once I saw Norm do it on NYW. He used a 1" round nose to cut his cove and it seemed to do a wonderful job. It would scare me to death to think about that big cutter whirling under the wood which can break at any time as Joe said. Try not to pass your hands or push blocks over the cutting area if you can help it.

[Steve D]

Yikes.... Call Woodguy, he just bought a moulder / planer. (it only average out to 1000 lbs when combined with the rest of his recent tool haul).

As already stated, use care. Also make sure that your stock and fences are flat and straight.

[sapwood]

Well, I'm probably in over my head here--but what the heck

I've used a taper jig riding along fence to cut a cove. By using featherboards, clamping, and whatever; and utilizing the handle on the taper jig I was able to keep my hands away from blade. The tapering jig also provided a bit more length than the fence alone does.

Does this sound dangerous?
Sapwood

[mkepke]

I use a basic set up consisting of two scrap guide boards clamped to the saw table with a Sears molding head with 1" radius knives.

My set up removes wood in a very..expeditious..manner (3HP saw and big knives on the molding head).

There are four basic parameters of the cove that you can modify:
1) the location of the cove in the board. You modify this by moving the guide boards forward or backward on the saw table relative to the leading AND trailing teeth of the blade

2) the height of the cove. Via the tablesaw height adjustment

3) arc of the cove. This one is tricky. It is a result of the angle of incidence formed between the guide boards and the saw blade. The more acute the angle, the 'tighter' the arc.

4) the evenness of the cove, i.e. whether it is an even cove or a lopsided cove. You vary the bevel angle setting of the saw blade.

I prefer using a molding head cutter since it is both stronger and cheaper than using a good blade.

Gooseneck cabinet scraper is a must for removing saw marks (as luck has it, Woodcraft has 'em on sale this week).

I agree that it is (never) a good idea to pass hands or pushblocks directly over the blade. An easy remedy is to screw some scrap plywood or even better lexan across the guide-boards thereby covering the blade.

-Mark

[D L Ames]

Thanks to all for your responses to this thread. I fully concur with all the comments on safety and the hazards associated with this type of operation. You're right Big Mike, a molding head cutter would be a big chuck of steel whirling away not far from the fingers......yikes.

Insom, that is a very informative link and helps me a bunch. I especially liked the chart laid out on that link that shows various profiles that can be formed by changing the angle of the fence and the bevel of the blade. That chart is worth printing and keeping on file out in the shop.

Sapwood, the technique you used sounds interesting but I am having a hard time visualizing it in my mind. Do you by chance have an pics of this set up we could look at?

Mark, thanks for your post outlining the parameters that effect the profile of the cove and how changes to these parameters modify the final outcome. I like the idea of adding a guard to the fences above the blade.

Bladeburner, good point about leaving enough wood at the bottom of the cove. I bet having the board snap halfway through would add a little too much excitement into one life and exactly the wrong moment.

D L

[mkepke]

Gratuitous cove molding shot. The beads on the top and bottom edges are made by bead cutters in the same molding head used for the cove itself.

The crack did not appear until AFTER I got .5" through the thickness. Oh well.

The wood is 5/4 red oak.

-Mark

[D L Ames]

Wow........great photo Mark. It's amazing to stand there and look at a tablesaw and even begin to imagine some of the things that it is capable of producing. Beautiful work.

D L

[McRabbet]

D L - There is an excellent, well-illustrated article on cutting coves on a table saw in Fine Woodworking, No 168 (January/February 2004) on pages 68-73. In addition to set-up methods, safety and "how-to's", the author has provided a method to establish the proper blade height, tilt angle and fence angles for cutting any cove you want. Originally in the form of an Excel spreadsheet, there is an online calculator on the Fine Woodworking website at http://www.taunton.com/finewoodworking/pages/nmw030.asp.

I also found a calculator you can download on Woodbin.com at http://www.woodbin.com/downloads/index.htm Cove safely!

I found another article in Woodworker's Journal (October 2003, pg 60-61) that includes an Excel spreadsheet formula to calculate fence angles for symmetrical coves given the desired depth and width.

Originally Posted by D L Ames

Thanks to all for your responses to this thread. I fully concur with all the comments on safety and the hazards associated with this type of operation. D L

[D L Ames]

Rob, Those are both dynamite and very informative links. Thanks for posting them.

D L